Page 122 - The Welfare of Cattle

breedInG and WeLfare 99

Vaccinating bulls against GnRH is an effective alternative to surgical castration as demonstrated
by the suppressed serum testosterone levels for over 100 days. Performance of the immunologically
castrated animals was intermediate between bulls and surgically castrated animals. The reduction
in testosterone production by testes in bulls also reduces their aggressive behavior and reduces risks
of injury to other animals and human handlers. Immunological castration using GnRH vaccine is a
welfare friendly alternative to achieve the same meat quality as for surgically castrated cattle.
Biotechnology and resistance to disease. Genetic engineering has potential to minimize and
control animal diseases—a critical component of animal welfare. Swine research efforts are under-
way to free the swine industry of porcine reproductive and respiratory syndrome virus (PRRSV).
Vaccines have not reduced the prevalence of this viral disease in pigs which results in producers
having to depopulate their farm of all pigs after an outbreak of PRRSV (see Niu et al., 2017; Prather
et al., 2017). CRISPR-Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats) and Cas9
(Cas9 is a biotechnology that allows modification of DNA to correct genetic mutations associated
with diseases including Down syndrome, spina bifida, anencephaly, and Turner and Klinefelter
syndromes in humans). CRISPR Cas9 is a biotechnology used to delete proteins on cell membranes
to make the cell and whole animal resistant to infection. Thus, genetic engineering is a valuable
tool to create animals resistant to disease. These technologies decrease production costs, enhance
sustainable agriculture and food security, and improve animal welfare.
Biotechnologies for enhancing animal health and animal production. The goal of sequencing
and mapping genomes of livestock is to establish linkages between inheritance of a desirable trait
(e.g., milk yield), and segregation of specific genetic markers coupled to that trait. The genetic
“tools” to accomplish this are increasingly sophisticated and include marker-assisted selection
based on quantitative trait loci (QTL), identification of a single-nucleotide polymporphism (SNP)
within QTL, gene editing, and genetic modification. A QTL may serve as a marker associated with
a gene(s) of interest, for resistance to disease or a production trait. For example, the difference in
size of dogs (e.g., Great Dane versus Chihuahuas) is due, in part, to differences in frequency of a
single allele of insulin-like growth factor 1 (IFG1) (Sutter et al., 2007). Thus, minor changes in gene
expression can have large impacts on animal growth, health, productivity, and behavior.
There are also genetic markers (QTL) for production traits in dairy cattle (see Weller and Ron,
2011), litter size in swine (King et al., 2003), and twinning rate in beef cows (Allan et al., 2007).
Current technologies coupled with biopsy and genetic analyses of preimplantation blastocysts
allows for selection of blastocysts with the desired genotype to enhance genetic progress in breed-
ing programs. In addition, sexing of embryos and sorting of X-bearing and Y-bearing sperm will
also allow for producers to select the gender of their offspring—which can have large implications
for welfare—particularly in dairy cattle, as dairy steers require different management.
Genomics biology has moved beyond sequencing of the genome to defining desirable gene
products across different tissues or conditions (Mortazavi et al., 2008). Therefore, it is used to
monitor gene expression for cell growth and differentiation, track gene expression changes during
development, and assess differences in gene expression among different tissues. That information
generated is used to advance understanding of genes associated with development, normal physi-
ological changes, differences between diseased and normal tissues, and classification of disease
states (Wang et al., 2009). Copy number variation (CNVs) refer to differences in the number of cop-
ies of a gene due to deletions or duplications of genes. Knowledge of CNVs influences the amount
of a gene product that may influence resistance to diseases or desired production traits in livestock
(Conrad et al., 2010).
The use of genome-based biotechnologies to enhance both animal health and animal production
characteristics is desirable because natural biological variation can be harnessed and used to its full
potential within a population. This is done by comparing genomics among animals that are resis-
tant to or susceptible to disease or that have high- versus low-production traits (e.g., milk yield) and
then using genetic markers to select for the desired phenotype. Then the use of genomic markers in